The present invention relates to a derivative of a mitogen-activated protein (MAP) kinase kinase and the use of said derivative for increasing disease resistance and enhanced stress tolerance in plants.
Signaling mechanisms that mediate plant defense responses may be strongly conserved among plants. This is supported by the observation that several classes of R genes confer disease resistance when expressed in heterologous plant species. For instance, the tomato disease resistance gene. Cf-9, was shown to confer responsiveness to the fungal avirulence gene product Avr9 in transgenic tobacco and potato (Hammond-Kosack et al., 1998). Although Cladosporium fulvum is exclusively a fungal pathogen of tomato, a rapid hypersensitive response (HR) was induced in transgenic tobacco and potato by experimentally allowing these specific interactions to occur which then induced signaling pathways that could be common to the plants. Furthermore, the tomato disease resistance gene, Pto, which specifies race-specific resistance to the bacterial pathogen Pseudomonas syringase pv tomato carrying the avrPto gene, also increased the resistance of tomato to Xanthomonas campestris pv vesicatoria and Cladosporium fulvum when over expressed (Tang et al., 1999). Clearly, it is the recognition of the pathogen that is unique to most plant species; whereas, the defense response is similar among them.
Considerable progress has now been made in understanding the signal transuction pathways following perception of biotic and abiotic stresses and the information is being used to develop strategies for modifying transgenic plants. Separate manipulations of the G protein pathway (Xing et al., 1996, 1997) may elevate pathogen resistance or induce defense reactions in transgenic tobacco (Beffa et al., 1995) and increase resistance to tobacco mosaic virus infection (Sano et al., 1994). Multiple roles for MAPK (mitogen-activated protein kinase) in plant signal transduction have also been shown, including responsiveness to pathogens, wounding and other abiotic stresses, as well as plant hormones such as ABA, auxin and ethylene (Hirt, 1997; Kovtun et al., 1998). MAPKK (mitogen-activated protein kinase kinase) from Arabidopsis (AtMEK1) and tomato (LeMEK1) have been shown to be induced by wounding (MNorris et al., 1997; Hackett et al., 1998), and the malze (ZmMEK1) gene was induced by high salinity and cold (Hardin and Wolniak, 1998). These enzymes interact within MAP kinase pathways that are extensively used for transcytoplasmic signaling to the nucleus. In the MAPK signal transduction cascade, MAPKK (MAP kinase kinase) is activated by upstream MAPKKK (mitogen-activated protein kinase kinase kinase) and in turn activates MAPK. The transcription of specific genes is induced by MAPK through phosphorylation and activation of transcription factors. This pathway has not yet been manipulated in plants.
The present invention relates to a derivative of a mitogen-activated protein (MAP) kinase kinase and the use of said derivative for increasing disease resistance and enhanced stress tolerance in plants.
According to the present invention it was determined that mutagenesis of a core phosphorylation site of a member of the MAPK cascade can create a permanently-active form, which stimulates both pathogen- and wound-inducible genes when introduced into plant cells.
Thus, according to the present invention there is provided a nucleic acid sequence encoding a derivative of a mitogen-activated protein kinase kinase gene from plants, wherein said derivative contains a negative charge in a core phosphorylation site of said protein kinase kinase gene.
Further according to the present invention there is provided a derivative of a mitogen-activated protein kinase kinase gene from plants, wherein said derivative contains a negative charge in a core phosphorylation site of said protein kinase kinase gene.
In a further embodiment of the present invention there is provided a cloning vector comprising a nucleic acid sequence encoding a derivative of a mitogen-activated protein kinase kinase gene from plants, wherein said derivative contains a negative charge in a core phosphorylation site of said protein kinase kinase gene.
The present invention also includes a transgenic plant comprising a nucleic acid sequence encoding a derivative of a mitogen-activated protein kinase kinase gene, wherein said derivative contains a negative charge in a core phosphorylation site of said protein kinase kinase gene.
Further, according to the present invention there is provided a method of increasing disease resistance or enhancing stress tolerance in a plant by introducing into said plant a nucleic acid sequence encoding a derivative of a mitogen-activated protein kinase kinase gene, wherein said derivative contains a negative charge in a core phosphorylation site of said protein kinase kinase gene.